Photos not syncing to Macbook Pro

[Dr. McKay]

For some reason, my iCloud photo library stopped syncing with my Macbook Pro.
Pictures I take on my phone sync perfectly fine with iCloud (I've checked on icloud.com, all is well) and all my devices, except for my Macbook Pro. Been like this for two days now.

My devices :
- 27 inch iMac 2017, latest version of Big Sur : syncs just fine
- iPhone 8 Plus, iOS 15 : syncs just fine
- iPad Pro 12.9 inch 2nd Gen, iOS 15 : syncs just fine
- Macbook Pro 15 inch 2015, latest version of Big Sur : latest sync was from two days ago, since then, nothing gets synced anymore.

I could log out of iCloud on the MB Pro, but then it asks me if I want to either download all photos to my mac or delete them ; my library is around 150Gb so I'd rather not do that, and if I delete them locally on my MB Pro, I wouldn't want it to sync an empty photos library back to iCloud, wiping everything everywhere (you never know).

Any suggestions ?

 

[Dr. McKay]

Sigh...
Logged out of iCloud on my MB Pro, of course all of my desktop files which were synced with iCloud disappeared.
However, when logging back in, they don't reappear, so no syncing from iCloud.

i've checked my profile in preferences, everything is activated... I don't get it.